1. Field of the Invention
This invention relates to a charge coupled device, and particularly to a charge coupled device (CCD) of a non-interlacing type which performs frame interline transfer (FIT).
2. Description of the Background Art
FIG. 9 depicts a conventional charge coupled device of a non-interlacing type. As illustrated in FIG. 9, the conventional charge coupled device includes first, second and third polysilicon electrodes 1, 2, and 3 and aluminum electrodes 4, 5 and 6. The polysilicon electrodes 1, 2 and 3 contact the aluminum electrodes 4, 5 and 6 at distal ends thereof, respectively. In FIG. 9, numeral 7 represents a picture element composed of a photodiode. FIG. 10 is a sectional view of the conventional charge coupled device, taken along line A-A in FIG. 9.
In such a structure of the conventional charge coupled device, a distance between the distal ends of the respective polysilicon electrodes, at which each polysilicon electrode contacts the corresponding aluminum electrode, is not short enough to effect high-speed transfer of signal charges. The conventional CCD using polysilicon electrodes cannot, therefore, transfer signal charges at high speed due to a high electrical resistance of polysilicon.
In order to overcome such drawbacks, there has been proposed a non-interlacing type charge coupled device which uses polysilicon electrodes coated with a low resistivity material, for instance tungsten. However, such a non-interlacing type CCD cannot perform frame interline transfer (FIT) which must be effected at a speed 40 to 100 times faster than that for interline transfer (IT). Such high-speed transfer cannot be realized by only reducing the resistance of the electrodes.